Physiological monitoring system featuring floormat and wired handheld sensor

ABSTRACT

A physiological monitoring system features a Floormat and Handheld Sensor connected by a cable. A user stands on the Floormat and grips the Handheld Sensor. These components measure time-dependent physiological waveforms from a user over a conduction pathway extending from the user&#39;s hand or wrist to their feet. The Handheld Sensor and Floormat use a combination of electrodes that inject current into the user&#39;s body and collect bioelectric signals that, with processing, yield ECG, impedance, and bioreactance waveforms. Simultaneously, the Handheld Sensor measures photoplethysmogram waveforms with red and infrared radiation and pressure waveforms from the user&#39;s fingers and wrist, while the Floormat measures signals from load cells to determine ‘force’ waveforms to determine the user&#39;s weight, and ballistocardiogram waveforms to determine parameters related to cardiac contractility. Processing these waveforms with algorithms running on a microprocessor yield the vital sign, hemodynamic, and biometric parameters.

BACKGROUND AND FIELD OF THE INVENTION

1. Field of the Invention

The invention relates to sensors that measure physiological signals froma patient (e.g. a user), and the use of such sensors.

2. General Background

Physiological sensors, such as vital sign monitors, typically measuresignals from a user to determine time-varying waveforms, e.g. thoracicbio-impedance (TBI), bio-reactance (BR), and electrocardiogram (ECG)waveforms, with electrodes that attach to the user's skin. Thesewaveforms can be processed/analyzed to extract other medically relevantparameters such as heart rate (HR) and heart rate variability (HRV),respiration rate (RR), stroke volume (SV), cardiac output (CO), andinformation relating to thoracic fluid content, e.g. thoracic fluidindex (TFC) and general body fluids (Fluids). Certain physiologicalconditions can be identified from these parameters using one-timemeasurements; other conditions require observation of time-dependenttrends in the parameters in order to identify the underlying condition.In all cases, it is important to measure the parameters with highrepeatability and accuracy.

Some conditions require various physiological parameters to be measuredover a relatively short period of time in order to identify thecondition. For example, Holter monitors can characterize various typesof cardiac arrhythmias by measuring HR, HRV, and ECG waveforms overperiods ranging from a day to a few weeks. On the other hand, chronicdiseases such as congestive heart failure (CHF) and end-stage renaldisease (ESRD) typically require periodic measurements of Fluids andweight throughout the user's life in order to identify the condition.Not surprisingly, user compliance with measurement routines typicallydecreases as the measurement period increases. This is particularly truewhen measurements are made outside of a conventional medical facility,e.g., at the user's home or in a residential facility such as a nursinghome.

Furthermore, the measured values of some physiological parameters willvary with the location at which the parameters are measured, while thoseassociated with other physiological parameters are relativelyindependent of the location at which the parameters are measured. Forexample, parameters such as HR, which depends on the time-dependentvariation of R-R intervals associated with QRS complexes in ECGwaveforms, are relatively insensitive to sensor positioning. Likewise,pulse oximetry (SpO2) and pulse rate (PR), as measured fromphotoplethysmogram (PPG) waveforms with a pulse oximeter, show littlevariance with measurement location.

On the other hand, measurements that depend on amplitude-dependentfeatures in waveforms, such as TFC or Fluids, will be strongly dependenton the measurement location, e.g. the positioning of electrodes. In thecase of TFC, for example, the measured value depends strongly on thesensed impedance between a set of electrodes. And this, in turn, willvary with the electrodes' placement. TFC deviation in the day-to-dayplacement of the electrodes can result in measurement errors. This, inturn, can lead to misinformation (particularly when trends of themeasured parameters are to be extracted), thereby nullifying the valueof such measurements and thus negatively impacting treatment.

Like TFC, measured values of blood pressure (BP), such as systolic(SYS), diastolic (DIA), and pulse (PP) pressures are typically sensitiveto the location at which the parameter is measured. For example, bloodpressure measured at the brachial artery with a sphygmomanometer (i.e. amanual blood pressure cuff) or with an oscillometric device (i.e. anautomated blood pressure cuff measuring oscillometric waveforms) willtypically be different from that measured at other locations on thebody, such as the wrist, thigh, finger, or even the opposite arm. Meanarterial pressure (MAP) is less sensitive to position, as it isrelatively constant throughout the body. Body (e.g. skin) temperature issimilarly dependent on the location at which it is measured, althoughcore temperature (TEMP), as measured from the ear or mouth, isrelatively consistent.

3. Sensors, Devices, and Relevant Physiology

Disposable electrodes that measure ECG and TBI waveforms are typicallyworn on the user's chest or legs and include: i) a conductive hydrogelthat contacts the user's skin; ii) an Ag/AgCl-coated eyelet thatcontacts the hydrogel; iii) a conductive metal post that connects to alead wire or cable extending from the sensing device; and iv) anadhesive backing that adheres the electrode to the user. Unfortunately,during a measurement, the lead wires can pull on the electrodes if thedevice is moved relative to the user's body, or if the user ambulatesand snags the lead wires on surrounding objects. Such pulling can beuncomfortable or even painful, particularly where the electrodes areattached to hirsute parts of the body, and this can inhibit usercompliance with long-term monitoring. Moreover, these actions candegrade or even completely eliminate adhesion of the electrodes to theuser's skin, and in some cases completely destroy the electrodes'ability to sense the physiological signals at various electrodelocations.

Some devices that measure ECG and TBI waveforms are worn entirely on theuser's body. These devices have been developed to feature simple,patch-type systems that include both analog and digital electronicsconnected directly to underlying electrodes. Such devices, like theHolter monitors described above, are typically prescribed for relativelyshort periods of time, e.g. for a period of time ranging from a day toseveral weeks. They are typically wireless and include features such asBluetooth® transceivers to transmit information over a short distance toa second device, which then transmits the information via a cellularradio to a web-based system.

SpO2 values are almost always measured at the user's fingers, earlobes,or, in some cases, the forehead. In these cases, users wear an opticalsensor to measure PPG waveforms, which are then processed to yield SpO2and PR values. TEMP is typically measured with a thermometer insertedinto the user's mouth, or with an optical sensor featuring aninfrared-sensitive photodiode pointed into the user's ear.

Assessing Fluids, TFC, weight, and hydration status is important in thediagnosis and management of many diseases. For example, ESRD occurs whena user's kidneys are no longer able to work at a level needed forday-to-day life. The disease is most commonly caused by diabetes andhigh blood pressure, and is characterized by swings in SYS and DIA alongwith a gradual increase in Fluids throughout the body. Users sufferingfrom ESRD typically require hemodialysis or ultrafiltration to removeexcess Fluids. Thus, accurate measurement of this parameter and/or TFCto characterize ESRD can eliminate the need for empirical clinicalestimations that often lead to over-removal or under-removal of fluidsduring dialysis, thereby preventing hemodynamic instability andhypotensive episodes (Anand et al., “Monitoring Changes in Fluid StatusWith a Wireless Multisensor Monitor: Results From the Fluid RemovalDuring Adherent Renal Monitoring (FARM) Study,” Congest Heart Fail.2012; 18:32-36). A similar situation exists with respect to CHF, whichis a complicated disease typically monitored using a “constellation” ofphysiological factors, e.g., fluid status (e.g. Fluids, TFC), vitalsigns (i.e., HR, RR, TEMP, SYS, DIA, and SpO2), and hemodynamicparameters (e.g. CO, SV). Accurate measurement of these parameters canaid in managing users, particularly in connection with dispensingdiuretic medications, and thus reduce expensive hospital readmissions(Packer et al., “Utility of Impedance Cardiography for theIdentification of Short-Term Risk of Clinical Decompensation in StableUsers With Chronic Heart Failure,” J Am Coll Cardiol 2006; 47:2245-52).

CHF is a particular type of heart failure (HF), which is a chronicdisease driven by complex pathophysiology. In general terms, HF occurswhen SV and CO are insufficient to adequately perfuse the kidneys andlungs. Causes of this disease are well known and typically includecoronary heart disease, diabetes, hypertension, obesity, smoking, andvalvular heart disease. In systolic HF, ejection fraction (EF) can bediminished (<50%), whereas in diastolic HF this parameter is typicallynormal (>65%). The common signifying characteristic of both forms ofheart failure is time-dependent elevation of the pressure within theleft atrium at the end of its contraction cycle, or left ventricularend-diastolic pressure (LVEDP). Chronic elevation of LVEDP causestransudation of fluid from the pulmonary veins into the lungs, resultingin shortness of breath (dyspnea), rapid breathing (tachypnea), andfatigue with exertion due to the mismatch of oxygen delivery and oxygendemand throughout the body. Thus, early compensatory mechanisms for HFthat can be detected fairly easily include increased RR and HR.

As CO is compromised, the kidneys respond with decreased filtrationcapability, thus driving retention of sodium and water and leading to anincrease in intravascular volume. As the LVEDP rises, pulmonary venouscongestion worsens. Body weight increases incrementally, and fluids mayshift into the lower extremities. Medications for HF are designed tointerrupt the kidneys' hormonal responses to diminished perfusion, andthey also work to help excrete excess sodium and water from the body.However, an extremely delicate balance between these two biologicaltreatment modalities needs to be maintained, since an increase in bloodpressure (which relates to afterload) or fluid retention (which relatesto preload), or a significant change in heart rate due to atachyarrhythmia, can lead to decompensated HF. Unfortunately, thiscondition is often unresponsive to oral medications. In that situation,admission to a hospital is often necessary for intravenous diuretictherapy.

In medical centers, HF is typically detected using Doppler/ultrasound,which measures parameters such as SV, CO, and EF. In the homeenvironment, on the other hand, gradual weight gain measured with asimple weight scale is likely the most common method used to identifyCHF. However, by itself, this parameter is typically not sensitiveenough to detect the early onset of CHF—a particularly important stagewhen the condition may be ameliorated simply and effectively by a changein medication or diet.

SV is the mathematical difference between left ventricular end-diastolicvolume (EDV) and end-systolic volume (ESV), and represents the volume ofblood ejected by the left ventricle with each heartbeat; a typical valueis about 70-100 mL. CO is the average, time-dependent volume of bloodejected from the left ventricle into the aorta and, informally,indicates how efficiently a user's heart pumps blood through theirarterial tree; a typical value is about 5-7 L/min. CO is the product ofHR and SV.

CHF users—particular those suffering from systolic HF—may receiveimplanted devices such as pacemakers and/or cardioverter-defibrillatorsto increase EF and subsequent blood flow throughout the body. Thesedevices may include circuitry and algorithms to measure the electricalimpedance between different leads of the device. Some implanted devicesprocess this impedance to calculate a “fluid index”. As thoracic fluidincreases in the CHF user, the impedance typically is reduced, and thefluid index increases.

4. Clinical Solutions

Many of the above-mentioned parameters can be used as early markers orindicators that signal the onset of CHF. EF is typically low in userssuffering from this chronic disease, and it can be further diminished byfactors such as a change in physiology, an increase in sodium in theuser's diet, or non-compliance with medications. This is manifested by agradual decrease in SV, CO, and SYS that typically occurs between twoand three weeks before hospitalization becomes necessary to treat thecondition. As noted above, the reduction in SV and CO diminishesperfusion to the kidneys. These organs then respond with a reduction intheir filtering capacity, thus causing the user to retain sodium andwater and leading to an increase in intravascular volume. This, in turn,leads to congestion, which is manifested to some extent by a build-up offluids in the user's thoracic cavity (e.g. TFC). Typically, a detectableincrease in TFC occurs about 1-2 weeks before hospitalization becomesnecessary. Body weight increases after this event (typically by betweenthree and five pounds), thus causing fluids to shift into the lowerextremities. At this point, the user may experience an increase in bothHR and RR to increase perfusion. Nausea, dyspnea, and weight gaintypically grow more pronounced a few days before hospitalization becomesnecessary. As noted above, a characteristic of decompensated HF is thatit is often unresponsive to oral medications; thus, at this point,intravenous diuretic therapy in a hospital setting often becomesmandatory. A hospital stay for intravenous diuretic therapy typicallylasts about 4 days (costing several thousands of dollars per day, ormore), after which the user is discharged and the above-described cyclemay start over once again.

Such cyclical pathology and treatment is physically taxing on the user,and economically taxing on society. In this regard, CHF and ESRD affect,respectively, about 5.3 million and 3 million Americans, resulting inannual healthcare costs estimated at $45 billion for CHF and $35 billionfor ESRD. CHF users account for approximately 43% of annual Medicareexpenditures, which is more than the combined expenditures for all typesof cancer. Somewhat disconcertingly, roughly $17 billion of this isattributed to hospital readmissions. CHF is also the leading cause ofmortality for users with ESRD, and this demographic costs Medicarenearly $90,000/user annually. Thus, there understandably exists aprofound financial incentive to keep users suffering from these diseasesout of the hospital. Starting in 2012, U.S. hospitals have beenpenalized for above-normal readmission rates. Currently, the penalty hasa cap of 1% of payments, growing to over 3% in the next 3 years.

Of some promise, however, is the fact that CHF-related hospitalreadmissions can be reduced when clinicians have access to detailedinformation that allows them to remotely titrate medications, monitordiet, and promote exercise. In fact, Medicare has estimated that 75% ofall users with ESRD and/or CHF could potentially avoid hospitalreadmissions if treated by simple, effective programs.

Thus, in order to identify precursors to conditions such as CHF andESRD, physicians can prescribe physiological monitoring regimens tousers living at home. Typically, such regimens require the use ofmultiple standard medical devices, e.g. blood pressure cuffs, weightscales, and pulse oximeters. In certain cases, users use these devicesdaily and in a sequential manner, i.e., one device at a time. The userthen calls a central call center to relay their measured parameters tothe call center. In more advanced systems, the devices are still used ina sequential manner, but they automatically connect through ashort-range wireless link (e.g. a Bluetooth® system) to a “hub,” whichthen forwards the information to a call center. Often, the hub featuresa simple user interface that presents basic questions to the user, e.g.questions concerning their diet, how they are feeling, and whether ornot medications were taken.

Ultimately, however, and regardless of how sophisticated suchinstrumentation may be, in order for such monitoring to betherapeutically effective, it is important for the user to be compliantand use their equipment consistently. Poor compliance (e.g.less-than-satisfactory consistency) with the use of any medical devicemay be particularly likely in an environment such as the user's home ora nursing home, where direct supervision may be less than optimal. Ofcourse, the clinical usefulness of any monitoring approach requires thatthe physiological parameters it measures be accurate.

SUMMARY OF THE INVENTION

In view of the foregoing, it would be beneficial to provide a monitoringsystem that is suitable for home use. Particularly valuable would be asingle system, free of external components, that is wireless andconveniently measures a collection of vital signs and hemodynamicparameters. Ideally, such a system would feature a single device andonly reusable (i.e. no disposable) sensors. The device should be easy touse and feature a simple form factor that integrates into the user'sday-to-day activities. The monitoring system according to the invention,which facilitates monitoring conditions such as HF, CHF, ESRD, cardiacarrhythmias, and other diseases, is designed to achieve this very goal.

More specifically, the invention described herein is a system thatfeatures a Floormat and Handheld Sensor, electrically connected to eachother by a flexible, conductor-bearing cable, that operate in concertwith the user's mobile device. The cable-connected configurationfacilitates measurement of various physiological parameters over ameasurement pathway that is as long as possible. This, in turn, yieldstime-dependent waveforms with high signal-to-noise ratios and,ultimately, accurate physiological information.

The Floormat resembles a conventional bathroom scale. It connectsthrough the cable to the Handheld Sensor, which features a grip that theuser can easily hold while standing on the Floormat. Collectively thesecomponents measure an enhanced set of parameters that include: all vitalsigns (e.g. PR and/or HR, SpO2, RR, SYS, MAP, and DIA, and TEMP);hemodynamic parameters (SV, CO, Fluids); and biometric parameters(weight, body composition). The system transmits information through awireless interface to a web-based system, where a clinician can analyzeit to help diagnose a user.

The system—which is a combination of the Floormat and HandheldSensor—measures time-dependent PPG, pressure, ECG, TBI, and/or BRwaveforms easily and conveniently from a user. It processes thesewaveforms to determine the above-mentioned parameters. During operation,the user simply stands on the Floormat and holds or otherwise supportsthe Handheld Sensor with (or in the region of) either the left or righthand. This establishes an electrical conduction pathway that extendsfrom the user's hand and/or wrist to their feet. Over this pathway, theHandheld Sensor and Floormat use a combination of electrodes that injectcurrent into the user's body, and subsequently sense bioelectric signalsthat, with processing, yield ECG, TBI, and BR waveforms. Simultaneously,the Handheld Sensor measures PPG waveforms with both red and infraredradiation (PPG-RED, PPG-IR) and pressure waveforms from the user'sfingers and wrist, while the Floormat measures signals from embeddedload cells to determine ‘force’ waveforms to measure the user's weight,and ballistocardiogram (BCG) waveforms. BCG waveforms, in turn, can beprocessed to estimate parameters related to cardiac contractility. Thus,with just a single device, the system measures the followingsynchronized, time-dependent waveforms: ECG, TBI, BR, PPG-RED, PPG-IR,force, and BCG. Processing these waveforms with algorithms running on amicroprocessor yields the vital sign, hemodynamic, and biometricparameters described above. Clinicians can analyze these parameters,which the system sends wirelessly to a web-based system, to diagnose auser in their home environment. In this and other ways, the combinedFloormat and Handheld Sensor provides an effective tool forcharacterizing users with chronic diseases, such as CHF, ESRD, andhypertension.

The Floormat and Handheld Sensor are designed, respectively, to resemblea conventional bathroom scale and a hand-held grip used, e.g., in aconventional video game controller. Most users are familiar with suchdevices, and thus use of the system should be intuitive. To makemeasurements, the user only needs to step on the Floormat and grip theHandheld Sensor. Total measurement time is about 30-60 seconds, afterwhich a simple user interface featuring, e.g., light-emitting diodes(LEDS) and/or a vibrating ‘buzzer’ indicates the measurement is completeand that the user can step off the Floormat and release the HandheldSensor. Such ease of use may increase compliance, which in turn yieldsthe daily measurements that are required to diagnose and effectivelytreat most chronic diseases.

In one aspect, the invention provides a system for measuring a user's COvalue. The system features: 1) a Floormat configured to rest on a flatsurface and supporting at least two electrodes and at least one loadcell, wherein the load cell is further configured to generate a forcewaveform; and 2) a Handheld Sensor connected to the Floormat through acable and featuring at least two electrodes. Within either the HandheldSensor or the Floormat (or both) is a circuit board including an analogimpedance system connected to the electrodes. The analog impedancesystem is configured to inject electrical current into the user throughone electrode in the Floormat and one electrode in the Handheld Sensor,sense signals through separate electrodes in the Floormat and HandheldSensor, and in response generate both impedance and ECG waveforms.

A first processing system (e.g., a microprocessor running computer code)in the system processes a digitized version of the force waveform todetermine a weight value. A second processing system then processes adigitized version of the impedance waveform to determine an impedancepulse, and further processes the impedance pulse and the weight value todetermine a SV value, as is described in detail below. A thirdprocessing system processes a digitized version of the ECG waveform todetermine an ECG pulse, and then further processes the ECG pulse todetermine an HR value. And finally, a fourth processing systemcollectively processes the SV and HR values to determine the CO value.

In embodiments, the Floormat's electrodes are disposed on a top surfaceso that they contact the user's foot when the user stands on theFloormat. The Handheld Sensor's electrodes are disposed on a gripconnected to the Handheld Sensor so that they contact the user's handwhen the user holds the Handheld Sensor. Thus, when the user operatesthe system, they have electrodes contracting their hands and feet.Suitably, electrodes in both the Floormat and Handheld Sensor include atleast one of the following: a conductive fabric, a metal, a conductivefoam, a hydrogel material, a conductive ink, a conductive rubber.

In other embodiments, the cable is flexible and includes a set ofconducting wires that connect electrodes in the Handheld Sensor and/orFloormat to the analog impedance system, which as described above istypically included on a circuit board enclosed by one (or both) of thesecomponents. In embodiments, the cable is a retractable cable thatretracts into the Floormat.

Different algorithms may be run by the system according to theinvention. Typically, such algorithms are operated by compiled computercode running on a microprocessor disposed on a circuit board within thesystem. For example, in one embodiment, the algorithm operates on thefirst processing system to calculate a volume conductor (V_(c)) from aninverse of the weight value. Another algorithm runs on the secondprocessing system to calculate a left ventricular ejection time from theimpedance pulse. Additionally, the second processing system calculates(dΔZ/dt)_(max) from the impedance pulse, and Z₀ from the baseline of theimpedance waveform. Using these parameters, the first processing systemcalculates SV from equations similar to those described in more detailbelow, or mathematical equivalents thereof.

In other embodiments, an algorithm operating on the third processingsystem analyzes the ECG pulse to determine an ECG QRS complex from whichit calculates HR. Finally, an algorithm operating on the fourthprocessing system calculates the CO value from a product of the SV andHR.

In another aspect, the invention provides a system for measuring aballistocardiogram pulse from a user. The system features a Floormat andHandheld Sensor similar to those described above. It also includes ananalog ECG system, connected to an electrode and an electrode in theHandheld Sensor, which generates an ECG waveform from signals sensedthrough these electrodes. The system features three processing systems,each running algorithms as described above. The first processing systemprocesses a digitized version of the ECG waveform to determine an ECGpulse, the second processing system process the force waveform todetermine a ballistocardiogram waveform, and the third processing systemcollectively processes the ECG pulse and the ballistocardiogram waveformto determine the ballistocardiogram pulse.

In embodiments, the ECG pulse determined by the first processing systemis a collection of ECG QRS complexes, and the third processing systemdetermines a first time segment associated with a time separating afirst point in time corresponding to a first ECG QRS complex, and asecond point in time corresponding to a second ECG QRS complex.Suitably, the R-wave of the first ECG QRS complex directly precedes theR-wave from the second ECG QRS complex, and the R-waves of the first andsecond ECG QRS complexes are separated in time by a period associatedwith a single heartbeat. The third processing system determines a secondtime segment associated with a time separating a third point in timecorresponding to a third ECG QRS complex, and a fourth point in timecorresponding to a fourth ECG QRS complex. Once these time segments aredetermined, the third processing system collectively processescorresponding segments of the BCG waveform to determine the BCG pulse.For example, the third processing system can sum (e.g. add) or averagethese segments to generate the ballistocardiogram pulse. In still otherembodiments, the system can include a fourth processing system thatprocess parameters associated with the BCG pulse and a calibrationfactor to estimate parameters such as cardiac contractility, SV, CO, HR,and ejection fraction. The calibration factor, for example, can bedetermined from a large population study wherein BCG pulses and theabove-mentioned parameters are measured with known reference techniques,and then analyzed with a mathematical model to determine the factor.

In another aspect, the invention provides a system for measuring a BPvalue from a user featuring a Floormat and Handheld Sensor similar tothose described above. The system features analog ECG, optical, andpressure systems that measure, respectively, ECG, PPG, and pressurewaveforms from the user. First and second processing systems processdigitized versions of the ECG and PPG waveforms to determine pulses thatare collectively processed with a third processing system to determine atransit time. A fourth processing system processes the pressure waveformto determine a BP calibration. And a fifth processing system processesthe transit time and the BP calibration to determine the blood pressurevalue.

In embodiments, the first processing system determines a first timevalue corresponding to an ECG QRS complex within the ECG pulse, and thesecond processing system determines a second time value corresponding tothe PPG pulse. For example, the system can determine the second timevalue from the base, maximum amplitude, maximum slope, and/or maximum offirst mathematical derivative of the PPG pulse. In embodiments, thethird processing system determines the transit time from themathematical difference between the second and first time values. Thefourth processing system processes the pressure waveform to determineMAP, SYS, and/or DIA, and additionally a patient-specific relationshipbetween blood pressure and transit time. The blood pressure calibrationcan be determined from these values. In embodiments, the fifthprocessing system multiplies the transit time by the patient-specificrelationship between blood pressure and transit time to determine BP.Alternatively, the fifth processing system can add SYS to the product ofthe patient-specific relationship between blood pressure and transittime to determine BP.

In another aspect, the invention provides a system that can be used, forexample, to measure ECG and HR from a user. The invention included agenerally flat Floormat configured to rest stably on a generally flatsurface and to support the weight of a user standing on it. The Floormathas a first electrode disposed at an upper surface thereof and inposition to make contact with the sole of one of the user's feet whenthe user stands on the Floormat. The invention also includes a HandheldSensor configured to be supported at a region of one of the user'shands. The Handheld Sensor includes a second electrode disposed inposition to make contact with skin in the region of the user's hand whenit is held, and is connected to the Floormat through a cable having oneor more internal electrical conductors. The system further includes ananalog system configured to receive biometric signals from the first andsecond electrodes and to process them to generate an analogphysiological waveform. A digital system is configured to digitize theanalog physiological waveform and to process it with computer code todetermine the physiological parameter. The analog system is located ineither the Floormat or the Handheld Sensor. Electrodes connect to theanalog system by means of the electrical conductors in the cable. Thisconfiguration facilitates obtaining signals across a conduction pathwaythat is substantially as long as possible.

In embodiments, the sensor system uses differential amplifiers togenerate analog waveforms, which include heartbeat-induced pulsations,e.g., ECG waveforms. HR can be determined from successive QRS complexesin the ECG waveforms. A processing system, i.e., a microprocessor andcomputer code that is executed on it, is located on a circuit board,which may be located in either the Floormat or the Handheld Sensor.

The Floormat suitably includes a load cell-based weight measurementsystem, to determine the user's weight.

The Handheld Sensor may include a grip by means of which the user canhold/support the Handheld Sensor, and one or more electrodes may belocated in the grip so that they contact the user's palm and/or anterior(i.e., palm-side) surfaces of the user's fingers when the user holds thegrip. Alternatively, the Handheld Sensor may include an arm-receivingportion, which could be as simple as a ring-shaped portion to encircleand be supported by the user's wrist without need for a grip, or itcould be formed as a pair of “wings” extending from a base portion fromwhich a grip extends. In this case, an inflatable pressure cuff issuitably provided in the arm-receiving portion to measure BPmechanically (i.e., by sensing and analyzing actual pressure valuesand/or waveforms), and the cuff could be configured to encircle theuser's wrist (in the case of a ring-shaped arm-receiving portion).Alternatively, the inflatable pressure cuff could be configured as twoopposing inflatable bladders that face each across a wrist-receivingspace within the arm-receiving portion. The electrode would then beprovided as an inflatable electrode, e.g., by providing elasticallystretchable, electrically conductive material over the inflatablebladder(s).

In another aspect, the invention provides a system for monitoring SVfrom a user. The system includes a generally flat Floormat configured torest stably on a generally flat surface and to support the weight of auser standing on it. The Floormat includes first and second electrodesdisposed at an upper surface thereof, which are positioned (e.g.,exposed at the upper surface) to make contact with the sole of one ofthe user's feet when the user stands on the Floormat. The system furtherincludes a Handheld Sensor configured to be supported at a region of oneof the user's hands (e.g., grasped by the hand or simply encircling thewrist akin to a bracelet). The Handheld Sensor includes third and fourthelectrodes disposed in position to contact with skin in the region ofthe user's hand when it is held. In this case, the Handheld Sensor iselectrically connected to the Floormat through a cable having one ormore electrical conductors disposed therein.

The first and third electrodes are configured to inject electricalcurrent into the user at their respective points of contact, and thesecond and fourth electrodes are configured to sense first and secondbiometric signals, respectively, which are induced by the injectedelectrical current. The biometric sensor system further includes a firstanalog system configured to receive the first and second biometricsignals and to process them to generate first and second analogphysiological waveforms, and a digital system configured to digitize theanalog physiological waveforms and to process them with computer code todetermine a physiological parameter such as SV.

In embodiments, the system features an impedance-measuring systemcomprised by the four electrodes and differential amplifiers to measurea set of analog impedance values that are digitized and processed toform a TBI or BR waveform having heartbeat-induced pulsations. Aprocessing system that can be part of the Floormat or the HandheldSensor receives a weight value from the Floormat and the TBI or BRwaveforms and then processes this information to calculate SV.

Furthermore, the system may operate by calculating a derivativedΔZ(t)/dt of an impedance waveform and determining a maximum value ofthe dΔZ(t)/dt waveform; an area of a pulse in the dΔZ(t)/dt waveform; anejection time from the dΔZ(t)/dt waveform; a maximum value of thedΔZ(t)/dt waveform ((dΔZ(t)/dt)_(max)); a left ventricular ejection time(LVET) from the dΔZ(t)/dt waveform; and a baseline impedance Z₀. SV maythen be determined from the equation:

${S\; V} = {V_{c} \times \frac{\left( {d\; \Delta \; {{Z(t)}/{dt}}} \right)_{\max}}{Z_{o}} \times L\; V\; E\; T}$

where V_(c) is a volume conductor, as described above, that may becalculated from a weight value that is suitably obtained via a loadcell-based system in the Floormat. Alternatively, stroke volume may bedetermined from the equation:

${S\; V} = {V_{c} \times \sqrt{\frac{\left( {d\; \Delta \; {{Z(t)}/{dt}}} \right)_{\max}}{Z_{o}}} \times L\; V\; E\; T}$

where, V_(c) is the volume conductor described above.

In another aspect, the invention provides a system for measuring SpO2featuring a Handheld Sensor with optical components; a Floormat systemwith circuit components for processing signals from the opticalcomponents; and a cable electrically connecting the Floormat and theHandheld Sensors. The Floormat includes a first electrode disposed at anupper surface thereof and in position to make contact with the sole ofone of the user's feet when the user stands on the Floormat. TheHandheld Sensor includes a second electrode that contacts skin in theregion of the user's hand (i.e., palm-facing surfaces of the fingers orthe wrist) when it is held; and a finger-receiving portion featuring anopening that receives the user's finger (typically located on the handgrasping the Sensor). Within the opening is an optical system thatincludes a first light source configured to irradiate the receivedfinger and a photodetector configured to receive radiation after itirradiates the received finger.

The inventive system according to this aspect of the invention furtherincludes a first analog system configured to receive biometric signalsfrom the first electrode and from the second electrode and to processthe biometric signals to generate a first analog physiological waveform;a second analog system configured to receive signals from thephotodetector and to process them to generate a second analogphysiological waveform; a first digital system configured to digitizethe first analog physiological waveform and to process it with computercode to determine a first physiological parameter in the set ofphysiological parameters; and a second digital system configured todigitize the second analog physiological waveform and to process it withcomputer code to determine a second physiological parameter in the setof physiological parameters. The first analog system is located ineither the Floormat or the Handheld Sensor and the electrode disposed inthe other device is electrically connected to the first analog system bymeans of the electrical conductors in the cable.

In embodiments, the system may be configured to generate and analyze PPGwaveforms, which include heartbeat-induced pulses. For example, computercode can identify the time between pulses in the PPG waveform todetermine the user's PR. Furthermore, computer code may be configured todetermine AD and DC components within the PPG waveform (including forred and infrared light wavelengths) and, from those components, a valueof SpO2.

In yet another aspect, the invention provides a system for measuring auser's BP, e.g. SYS, MAP, and DIA. To that end, the system is configuredgenerally as per the aspect of the invention described immediatelyabove. The system includes a first analog system configured to receivebiometric signals from the first electrode and from the second electrodeand to process the biometric signals to generate one of a bioimpedanceand a bioreactance signal that, with further processing, yields a firsttime-dependent physiological waveform. The system further includessystems to process signals from the photodetector to generate a secondphysiological waveform and to process the first and second waveforms todetermine the user's BP.

In yet another aspect, the invention features a system configured tomeasure BP using an inflatable bladder, e.g., via oscillometry. Here,the system features a Floormat and Handheld Sensor similar to thatdescribed above. Either component may include a microprocessor-basedpressure-control inflation system including a pressure sensor thatsenses air pressure in the inflatable cuff; an air pump; and a valve,with the pressure-control inflation system being configured and arrangedto control inflation and deflation of the inflatable bladder and the airpump being connected to the inflatable cuff via a tube extending alongthe cable member to the inflatable cuff. The biometric sensor systemfurther includes a first analog system configured to receive signalsfrom the pressure sensor and to process them to generate pressuresignals; and a processing system configured 1) to issue computercommands to the pressure-control system to inflate and deflate the cuffwhile the first analog system generates the pressure signals, and 2) toanalyze modulations in digital versions of the pressure signals toestimate SYS, MAP, and DIA.

In embodiments, the system includes computer code that filters thepressure signal and identifies oscillations therein. For example, theoscillation having a maximum amplitude value typically corresponds toMAP; oscillations having predetermined ratios when normalized by themaximum amplitude typically correspond to SYS and DIA. Furthermore, thecuff may be provided in an arm-receiving portion of the Handheld Sensor,either as inflatable bladders that face each other across awrist-receiving space in the arm-receiving portion or as an inflatablebladder disposed around an arm-encircling annular ring.

Suitably, the embodiments include electrodes on the upper surface of theFloormat and within the Handheld Sensor to facilitate measuring an ECGsignal. HR can be determined from the time difference between successiveQRS complexes in the ECG signal. Electrodes in the Handheld Sensor canbe located on a grip that supports the Sensor, or as inflatableelectrodes provided by means of elastically stretchable, conductivematerial that is stretched across a pair of inflatable bladders onopposing sides of the wrist-receiving space.

In yet another aspect, the invention features a system configured tomeasure BP using an inflatable bladder, e.g., via arterial occlusion.Here, the Handheld Sensor includes an optical system that measures a PPGwaveform from the user's fingers, and an inflation system featuring aninflatable cuff that applies pressure to the corresponding wrist.Gradual inflation of the cuff compromises blood flow to the fingers,thereby describing amplitudes of pulsations within the PPG waveforms.Analysis of the pulsations with analog and digital systems yields BPvalues, particularly MAP and SYS.

In embodiments, the system includes computer code configured to analyzepulsatile pressure signals to identify systolic pressure based on anamplitude of the pressure wave having a minimum value, where thepressure wave amplitudes may be estimated from a mathematical function.The system may also include computer code configured to analyzepulsatile pressure signals to identify mean arterial pressure based onan amplitude of the pressure wave having a maximum value, where thepressure wave amplitudes may be estimated from a mathematical function.

According to another aspect, the invention features a sensor configuredto measure a physiological parameter using a BCG signal generated fromthe user's feet, with QRS complexes in an ECG signal being used toidentify fiducial points on the BCG signal. Thus, according to thisaspect of the invention, a biometric sensor system includes a generallyflat floormat configured to rest stably on a generally flat surface andto support the weight of a user standing thereon, which includes aweight-measuring system having at least one load cell and an amplifiersystem configured to measure a time-dependent load-cell voltage from atleast one load cell and to process the time-dependent load-cell voltageto determine a time-dependent load-cell waveform; and a first electrodedisposed at an upper surface of the floormat and in position to makecontact with the sole of one of the user's feet when the user stands onthe floormat. The system further includes a handheld sensor configuredto be supported at a region of one of the user's hands, which includes asecond electrode disposed in position to make contact with skin in theregion of the user's hand when the handheld sensor is supported thereat;and which is connected to the floormat via a cable having one or moreelectrical conductors disposed therein. The system also includes ananalog system configured to receive biometric signals from the firstelectrode and from the second electrode and to process the biometricsignals to generate an ECG waveform including a series of QRS complexes,with the analog system being located in either the Floormat or theHandheld Sensor and the electrode that is disposed in the other devicebeing electrically connected to the analog system by means of theelectrical conductors in the cable, as well as a processing systemconfigured to receive the time-dependent load-cell waveform from thefloormat sensor and the ECG waveform from the analog system. Theprocessing system is further configured 1) to analyze the series of QRScomplexes in the ECG waveform to determine a set of fiducial markers,and then 2) to analyze the set of fiducial markers to average togethermultiple sections of the time-dependent load-cell voltage waveform todetermine the BCG signal from a user.

In embodiments, AC components may be isolated from the load cellwaveform, and then analyzed using an ECG waveform to identify fiducialpoints therein. Multiple waveform segments may be averaged to form anaverage waveform segment, which is then processed to identify a BCGpulse from which a physiological parameter of interest may bedetermined. In another aspect, the invention features a sensor fordetermining a physiological parameter (e.g. cardiac contractility) fromthe BCG pulse.

In embodiments, well-defined fiducial points, such as a pulse from theECG, PPG, IMP and/or BR waveforms, may be used to analyze the BCGsignal. One or more segments of the BCG signal could then be analyzed(e.g., by averaging multiple segments) to determine a physiologicalparameter of interest.

In another aspect, pulsatile components from time-dependent waveformsmeasured by the Floormat and Handheld Sensor can be collectivelyanalyzed to determine a pulse transit time (PTT). Such pulsations maybebe included in the ECG, PPG, TBI, BR, and/or BCG waveforms. The pulsetransit time is then used to calculate a BP value.

In another aspect, the invention features a biometric sensor systemhaving a Floormat and a Handheld Sensor generally as described above.The Floormat includes a load cell-based weight-measurement system and anelectrode disposed at its upper surface to contact the sole of one ofthe user's feet. The Handheld Sensor also includes an electrode, which,together with the Floormat sensor, is used to generate an ECG waveform.By processing a load cell waveform generated by the load cell system andthe ECG waveform, a given user using the system can be identified.

In another aspect, the invention features a biometric sensor systemhaving a Floormat and a Handheld Sensor generally as described above.The Floormat includes a load cell-based weight-measurement system. Aprocessing system receives and processes a time-dependent load-cellwaveform to identify user stability and/or palsy. In particular, aload-cell waveform with little variation in amplitude (e.g., below acertain predetermined threshold) and/or relatively low contribution fromhigh-frequency components (e.g., below a certain predeterminedthreshold) may be characterized as corresponding to a user that hasacceptable balance. On the other hand, a user with balance difficultiesor palsy may be identified by load-cell waveforms having a high degreeof amplitude variation (e.g., as expressed in terms of amplitudevariation as a percentage of a baseline or average value) or a highcontribution to the waveform from high-frequency components.

The measurement system described herein has many advantages.Collectively, the Floormat and Handheld Sensor provide a single,easy-to-use system that a user can deploy to measure all their vitalsigns, complex hemodynamic parameters, and basic wellness-relatedbiometric parameters such as weight, percent body fat, and muscle mass.Ideally the system is used in much the same way as a conventionalbathroom scale. Such ease of use may increase compliance, therebymotivating daily use. And with this, the measurement system cancalculate trends in a user's physiological parameters, thereby allowingbetter detection of certain disease states and/or management of chronicconditions such as HF, CHF, diabetes, hypertension, chronic obstructivepulmonary disease (COPD), ESRD, and kidney failure.

Still other advantages should be apparent from the following detaileddescription, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, side view of a user being monitored by the systemaccording to the invention, which includes a Floormat that the userstands on, a cable-connected Handheld Sensor that the user holds whilethey stand on the Floormat, and a mobile device that connects wirelesslyto the system and to a web-based system;

FIG. 2 is a schematic drawing showing a current conduction path andlocations on the human body were the Floormat and Handheld Sensorcollectively measure time-dependent, physiological waveforms from theuser;

FIG. 3 is a flow chart of an algorithm that the system of FIG. 1 uses tocalculate SV;

FIG. 4 is a photograph of internal components within the Floormat ofFIG. 1;

FIG. 5 is a photograph of the Floormat of FIG. 4, including a topportion to cove internal components shown in FIG. 4;

FIG. 6 is a three-dimensional, side view of the Handheld Sensor whereinthe Sensor's mechanical housing is shown as being transparent toindicate the Sensor's internal components;

FIG. 7 is a three-dimensional, exploded view of the Handheld Sensor andcomponents;

FIG. 8A is a photograph of the Handheld Sensor's electrodes, whichinclude inflatable bladders covered with a fabric that is bothstretchable and conductive, in an inflated state;

FIG. 8B is a photograph of the Handheld Sensor's electrodes shown inFIG. 8A in an uninflated state;

FIG. 9A is a plot of time-dependent ECG, ΔZ(t), and PPG waveformsmeasured via the Handheld Sensor and the Floormat; FIG. 9B is a plot oftime-dependent derivatives of the ΔZ(t) waveform (d(ΔZ(t))/dt) and PPGwaveform (d(PPG)/dt) shown in FIG. 9A, along with markers indication howVTT and PAT are calculated from these waveforms; and

FIG. 10 is a table showing various physiological conditions and how theyare predicted by trends in certain physiological parameters measured bythe system of FIG. 1.

DETAILED DESCRIPTION 1. System Overview

FIG. 1 shows a system 90 featuring a Floormat 200 and Handheld Sensor100, electrically connected to each other by a conductor-bearing cable102, that work in concert to measure a user 125 according to theinvention. Both the Floormat 200 and Handheld Sensor 100 feature acollection of physiological sensors that connect to the user 125, asdescribed in detail below, to measure time-dependent physiologicalwaveforms, and from these physiological parameters. A wireless device(e.g. a Bluetooth® radio) within the Floormat 200 transmits both thewaveforms and parameters to an external mobile device 120. The goal ofthe system 90 is to quickly and non-invasively measure all five vitalsigns (HR, RR, SpO2, BP, and TEMP), hemodynamic parameters (SV, CO, TFC,Fluids), and biometric parameters (weight, body composition) with asystem 90 that is easy-to-use, low-cost, inconspicuous, and seamlesslyconnects to the cloud. A rationale for the system 90 is that mostdisease states are predicted not by a single parameter (e.g. BP), butrather by a collection or ‘constellation’ of parameters that may trendin different directions. However a complicating factor in monitoringsuch parameters is that they typically cannot be measured with a singledevice, or from a single location on the body. Thus, the system 90 isdesigned to measure all the above-described parameters using as fewsensors as possible.

To measure ECG and TBI waveforms, the Floormat 200 includes two sets ofelectrodes 212A, 212B, 213A, 213B, as shown in FIGS. 1 and 5, and theHandheld Sensor 100 includes a single set of electrodes 150A, 150B, asshown in FIGS. 6, 8A, and 8B). All of the electrodes 212A, 212B, 213A,213B, 150A, 150B may be made from a common reusable material, mostpreferably a stretchable conductive fabric pulled over a soft substratesuch as foam, as is described in more detail below. The electrodescontact the user's skin during use, but do not adhere to it. Theyconnect through wires (i.e., conductors) to a circuit board 206 locatedwithin the Floormat 200. Collectively the electrodes 212A, 212B, 213A,213B, 150A, 150B establish a ‘conduction pathway’ over which bioelectricsignals are generated, collected, and eventually processed by thecircuit board 206 to measure ECG, TBI, and BR waveforms, described inmore detail below. More specifically, during a measurement theelectrodes 150A, 150B within the Handheld Sensor 100 inflate and contactthe user's wrist. They connect to the circuit board 206 through wires inthe cable 102, whereas the electrodes in the Floormat are in directelectrical contact with metal traces on the circuit board 206. (In analternate configuration, the circuit board 206 could be located in theHandheld Sensor 100 instead of the Floormat 200; in that case, theelectrodes in the Handheld Sensor 100 would be in direct electricalcontact with metal traces on the circuit board 206 and the electrodeswithin the Floormat 200 would connect to the circuit board 206 viaconductors in the cable 102.) One electrode 150A in the Handheld Sensor100 injects electrical current into the user's wrist, while the other150B senses a bioelectric signal related to the impedance (i.e.resistance) encountered by injected current. Similarly, one electrode212A in the Floormat 200 injects a similar electrical current into soleof, for example, the user's left foot, while the other 212B senses asimilar bioelectric signal. Such a measurement is typically referred toas bio-impedance, described in the following co-pending patentapplications, the contents of which are incorporated herein byreference: FLOORMAT PHYSIOLOGICAL SENSOR (U.S. Ser. No. ______, Filed______); COMBINED FLOORMAT AND BODY-WORN PHYSIOLOGICAL SENSORS (U.S.Ser. No. ______, Filed ______); HANDHELD PHYSIOLOGICAL SENSOR (U.S. Ser.No. ______, Filed ______); PHYSIOLOGICAL MONITORING SYSTEM FEATURINGFLOORMAT AND HANDHELD SENSOR (U.S. Ser. No. ______, Filed ______); andPHYSIOLOGICAL MONITORING SYSTEM FEATURING FLOORMAT AND WIRED HANDHELDSENSOR.

Current injected by the two electrodes 150A, 212A is typically modulatedat a relatively high frequency (e.g. 100 kHz) and low amperage(typically about 4-8 mA), and is out of phase by 180°. Both biometricsignals feed into circuits (e.g., differential amplifiers) on thecircuit board 206, which processes them to yield TBI waveforms featuringboth AC and DC components. Further processing of the AC componentsyields measurements of SV, CO, and RR, while that for the DC componentsyields measurements of Fluids and TFC, as described in more detailbelow.

The same bioelectric signals collected by the electrodes 150B, 212Bwithin, respectively, the Handheld Sensor 100 and Floormat 200 areadditionally processed by systems (i.e., circuits and computer codebeing executed on a microprocessor) the circuit board 206 to yield anECG waveform. With further processing (e.g. detection of R-R intervalsin neighboring QRS complexes), the ECG waveform yields HR and HRV. Tocounteract the well-known effects of noise caused by common-modefrequencies (typically present at 50 or 60 Hz, and caused by theelectrical grid), the electrode 213A contacting the user's right footinjects a low-amperage current modulated at the common-mode frequency.The injected current is typically 180° out of phase with the common-modenoise present in the unprocessed ECG waveform, and the amperage of thecurrent is modulated according to the level of the noise. This is thewell-known functionality of a ‘right-leg drive’ electrode and circuit.Suitably, the electrode 213B may have no function, and is simply presentto add symmetry to the configuration of electrodes on the Floormat's topsurface. Alternatively, the electrode 213B may be electrically connectedto its neighboring electrode 212B to collect additional bioelectricsignals for the ECG waveform.

With the inventive system described herein, the Floormat 200 andHandheld Sensor 100 work in concert to measure ECG, TBI, and BRwaveforms as measured across the user's entire body (i.e., hand tofoot), as opposed to just a relative small portion of the body (e.g.,thoracic cavity) as measured by previously known systems. Such ameasurement across a conduction pathway extending from the user's footto the user's hand region is particularly advantageous for measuring TBIwaveforms, which feature a DC component that is calculated over theconduction pathway and that is used to calculate TFC and Fluids. Arelatively large pathway, like that measured by the combination of theFloormat and Handheld Sensor, may be more indicative of full-bodyimpedance.

FIG. 2 shows a schematic drawing indicating how the inventive devicedescribed herein measures waveforms having pulsatile components alongdifferent portions of the user's body, with each portion separated fromthe source of the pulsatile components—the user's heart—by asequentially increasing distance. More particularly, the figure shows aschematic indication of whole-body measurements made with the combinedFloormat and Handheld Sensor, as described above. Here, the arrow 127indicates the conduction pathway over which bioelectric signals aremeasured to generate an ECG waveform 250 and the AC component of the TBIwaveform 253 (and, in embodiments, a similar component from BRwaveforms, although these are not shown in the figure). The AC componentof the TBI waveform 253, which is described in more detail below andreferred to as ΔZ, primarily indicates blood flow from the heart's leftventricle into the aorta. Electrodes in the Floormat measure thesewaveforms from a first distal point of the arrow 127, as indicated bycircles 260A, 260B, with the two circles indicating the pair ofelectrodes (one for current injection; one for sensing bioelectricsignals). Signals from these electrodes are combined with signalsmeasured by the electrodes in the Handheld Sensor at the other distalpoint of the arrow 127, as indicated by circles 263A, 263B, to measurethe ECG 250 and TBI 253 waveforms. The ECG waveform 250 features apulsatile component, called a QRS complex, which indicates initialelectrical activity in the user's heart and, informally, marks thebeginning of the cardiac cycle.

Simultaneously, optics (i.e. LEDs and a photodetector) within theHandheld Sensor measure pulsatile components in the PPG waveform 254,sampled from arteries within the user's thumb as indicated by the circle264. The PPG waveform 254 indicates a heartbeat-induced volumetricexpansion in the artery lying beneath the optics. The inflatableelectrodes in the Handheld Sensor, coupled with pressure-measuringelectronics, sense pulsatile components from a pressure waveform 255measured from the user's wrist as indicated by circle 265. Similar tothe PPG waveform 254, the pressure waveform 255 indicates aheartbeat-induced increase in pressure, primarily in the radial andulnar arteries. Finally, load cells in the Floormat measure BCGwaveforms 256 from a slight heartbeat-induced volumetric expansion inthe user's foot, as indicated by circle 266.

The Floormat 200 and Handheld Sensor 100 may each use parametersmeasured wholly or in part by the other device to complete their ownmeasurement. For example, ΔZ waveforms measured as described above mayuse weight or an SV calibration, as measured by the Floormat 200, todetermine SV. Likewise, ECG waveforms measured as described above may beused as a fiducial marker to perform a ‘beatstacking’ algorithm,described in more detail below, to measure BCG pulses.

FIG. 3, as an example, indicates an algorithm 160 featuring a first step(161) wherein the Floormat 200 measures and processes weight and bodycomposition to determine an ‘SV calibration’. Using a second step (162),the Floormat and Handheld Sensor collectively measure TBI waveforms,which during a third step (163) a computer processing unit (CPU),suitably located in the Floormat, processes with the SV calibration todetermine SV. The details of this algorithm are described in moredetail, below.

Referring again to FIG. 1, a Bluetooth® transmitter located in theFloormat 200 transmits information, as shown by arrow 110, to theexternal mobile device 120. The mobile device 120, for example, can be acellular telephone or tablet computer using a customized softwareapplication (e.g. one running on Android or iOS platforms, anddownloaded from the cloud). During a measurement, the mobile device 120is typically placed on a horizontal surface 130, such as a bathroomcountertop. Once it receives information, the mobile device 120transmits it to a Web-based System 118 for follow-on analysis, e.g. by aclinician or a data-analytics software platform.

2. Floormat

FIGS. 4 and 5 show, respectively, photographs of the internal componentsand a top portion of a Floormat 200 according to the invention.Resembling a conventional bathroom scale that is configured to reststably on a flat, horizontal surface, the Floormat 200 features metalbase 202 that supports four load cells 205A-D, each connected to metalfoot 204A-D located at a respective corner of the base 202, and a topsurface 201 that houses upwardly exposed electrodes 212A, 212B, 213A,213B for injecting current into the soles of the user's feet and sensingbioelectric signals, as described above. The metal feet 204A-D aredesigned to sit on a horizontal surface (e.g. a floor) to support theFloormat 200 so that the user can step onto it. During use, a voltage isapplied to each load cell using a 4-wire cable 216, held in place by aplastic tab 217, which connects to the circuit board 206. (Note thateach load cell connects to a unique 4-wire cable, which in turn is heldin place with a unique plastic tab; only one of these components isspecifically labeled/identified in the figure.) Each load cell 205A-Dincludes a Wheatstone Bridge (not shown in the figure), which is a4-resistor electrical circuit featuring one or more resistors having aresistivity that varies with strain caused by an applied weight, andconnects to the circuit board 206 with a unique 4-wire cable. A usersteps on the Floormat's top surface 201 so that the soles of their feetcontact each electrode 212A, 212B, 213A, 213B. Force caused by theuser's weight presses down against each load cell, causing therespective Wheatstone Bridge to generate a time-dependent voltage thatpasses through the 4-wire cable 216 to the circuit board 206, where itis processed by separate differential amplifiers associated with eachload cell to amplify the voltage resulting from the load cell'sWheatstone Bridge. The resulting voltages pass to a summing amplifier onthe circuit board 206, which adds and amplifies them to generate asingle voltage that is then processed by a microprocessor on the circuitboard to determine the user's weight.

Additionally, high-frequency signal components from the load cells205A-D can be further processed with the analog and digital electronicson the circuit board 206 to measure the BCG waveforms, which asdescribed above are generated by a slight, heartbeat-induced volumetricexpansion in the user's foot caused by blood ejected during systole. BCGwaveforms are typically best measured using signal-processing techniquessuch as beatstacking, as described above. The BCG waveforms can also becollectively analyzed with ECG and/or PPG waveforms to calculate atransit time, which relates inversely to BP as described in theabove-referenced patent application entitled ‘FLOORMAT PHYSIOLOGICALSENSOR’, the contents of which have been incorporated herein byreference.

In certain embodiments, time-dependent voltage waveforms measured by theload cells can be used to detect parameters such as balance and evenprogression of diseases such as Parkinson's disease. More specifically,a user that is swaying or undergoing related motions will generate awaveform that varies in amplitude over time; this may indicate a userwith ‘bad’ balance. Likewise, a user that stands in a stable, unwaveringmanner on the Floormat will generate a waveform featuring relativelystable amplitude over time, thus indicating ‘good’ balance. In a similarmanner, a user with Parkinson's disease typically undergoes small, rapidmovements or tremors that will map onto the time-dependent voltagewaveform. Analysis of frequency and amplitude components within thewaveforms may indicate the progression of this disease.

On its top surface 201, the Floormat 200 also includes a ‘status bar’208 that is raised relative to the top surface 201 and houses a trio ofstatus LEDs 217 indicating the Floormat's status, along with apushbutton on/off switch 209. The status LEDs 217 indicate, for example,if the Floormat: i) is ready for the user to step on it; ii) is making ameasurement; iii) is transmitting a measurement; or iv) has completed ameasurement. Other states of the Floormat, of course, can be indicatedwith the status LEDs 217. Each LED can emit a variety of colors and canbe driven to flash at different frequencies, making it possible toindicate a large number of configurations to the user. As indicated byits name, the pushbutton on/off switch 209 turns the Floormat 200 on andoff.

In a preferred embodiment, the Floormat 200 lacks a conventional display(e.g. an LCD). Instead it relies on the status LEDs to indicate theabove-mentioned operation states, and displays information on thesoftware application running on the mobile device. In alternateembodiments the Floormat may include a conventional display.

As noted above, the Handheld Sensor 100 connects to the Floormat 200 (inparticular, to the circuit board 206 and the processing componentscontained thereon) through a flexible cable 102. The cable 102 typicallyincludes six separate wires that connect to the circuit board andsupply: i) biometric signals from electrodes for the ECG and TBImeasurements; and ii) power and ground for an internal circuit boardthat powers the PPG and BP measurements. These components are describedin more detail with reference to FIGS. 6-8.

The Floormat's top surface 201 supports sets of electrodes 212A, 212B,213A, 213B that are secured to the metal base 202 with a pair of plasticarms 210, 211 that hold them securely in place during a measurement.Suitably, the electrodes 212A, 212B, 213A, 213B are reusable componentsfabricated from conductive materials such as stainless steel or foamcovered with a conductive fabric. Use of other electrode materials isalso within the scope of this invention.

Electrodes 212A, 212B, when combined with complementary electrodes inthe Handheld Sensor 100, are used for TBI and ECG measurements, asdescribed above. These measurements use circuitry within the circuitboard 206 that features one or more differential amplifiers connected tothe electrodes and which generate a time-dependent voltage. The voltagecan be filtered and processed with analog circuitry to measure ECG andTBI waveforms. Measuring ECG waveforms with this technique is known inthe art. To measure TBI waveforms, typically analog circuitry within thecircuit board 206 separates out an AC waveform that features relativelyhigh-frequency features (ΔZ(t)), and a DC waveform that featuresrelatively low-frequency features (this waveform is typically calledZ₀). This technique for measuring ΔZ(t) and Z₀ is described in detail inthe following co-pending patent applications, the contents of which havebeen previously incorporated herein by reference: “NECK-WORNPHYSIOLOGICAL MONITOR,” U.S. Ser. No. 62/049,279, filed Sep. 11, 2014;“NECKLACE-SHAPED PHYSIOLOGICAL MONITOR,” U.S. Ser. No. 14/184,616, filedFeb. 19, 2014; and “BODY-WORN SENSOR FOR CHARACTERIZING PATIENTS WITHHEART FAILURE,” U.S. Ser. No. 14/145,253, filed Dec. 31, 2013, and‘FLOORMAT PHYSIOLOGICAL SENSOR’, U.S.S.N FLOORMAT PHYSIOLOGICAL SENSOR(U.S. Ser. No. ______, Filed ______); COMBINED FLOORMAT AND BODY-WORNPHYSIOLOGICAL SENSORS (U.S. Ser. No. ______, Filed ______); HANDHELDPHYSIOLOGICAL SENSOR (U.S. Ser. No. ______, Filed ______); PHYSIOLOGICALMONITORING SYSTEM FEATURING FLOORMAT AND HANDHELD SENSOR (U.S. Ser. No.______, Filed ______); and PHYSIOLOGICAL MONITORING SYSTEM FEATURINGFLOORMAT AND WIRED HANDHELD SENSOR.

For example, respiratory effort (i.e. breathing) changes the capacitanceof the chest, thus imparting a series of low-frequency undulations(typically 5-30 undulations/minute) on the ΔZ(t) waveform. The HandheldSensor's digital system processes these oscillations to determine RR.

Fluids (e.g. TFC) also conduct the injected current, and thus Fluidlevels vary inversely with impedance levels: an increase in Fluid leveldecreases impedance, while a decrease in Fluid level increasesimpedance. Thus, fluids that accumulate in the thoracic cavity affectthe impedance within the conduction pathway in a low-frequency (i.e.slowly changing) manner, and can be detected by processing the Z₀waveform. Typically, the Z₀ waveform features an average value ofbetween about 10-30 Ohms, with 10 Ohms indicating relatively lowimpedance and thus high fluid content (e.g. the user is ‘wet’), and 30Ohms indicating a relatively high impedance and thus low fluid content(e.g. the user is ‘dry’). Time-dependent changes in the average value ofZ₀ can indicate that the user's fluid level is either increasing ordecreasing. An increase in fluid level, for example, may indicate theonset of CHF.

With calibration, the Z₀ waveform yields Fluid levels and changestherein, as concentrated in the user's lower extremities. Typically,changes in impedance parameters, which in turn indicate a correspondingchange in Fluid level, are more relevant than absolute impedance levels.

A similar approach is used for bio-reactance and BR waveforms. Howeverin this case, circuitry measures changes in phase corresponding to theinjected current, as opposed to changes in amplitude used forbio-impedance. During a measurement, the phase difference between theinjected currents and the detected currents is measured by thebio-reactance circuit and ultimately processed with the digital systemon the circuit board to generate the BR waveform. The difference inphase is due to the current being slowed down by the capacitiveproperties of cell membranes within the conduction pathway. The baselinephase difference (Φa) is estimated from the DC component of the BRwaveform. Φa is used to calculate tissue composition, described in moredetail below. The AC component of the waveform can be used to track RR,SV, and CO as described above.

Bio-reactance, when combined with bio-impedance, can measurephysiological parameters related to body composition (e.g. fat, muscle,and fluid in the user's body) and the progression of disease states.These parameters, like weight, may also be used to calibrate the SVmeasurement. Typically, such a calibration is determined by conducting alarge-scale clinical study using a known reference for SV and CO. Morespecifically, bio-impedance and bio-reactance measurements analyze theresistance and reactance of the user's tissue—along with biometricparameters such as height, weight and age—to generate accurate estimatesof the composition of the tissue in the abdomen, chest, and arm. Suchparameters may correlate with the size of the user's left ventricle andaorta, and can thus be used within V_(c). Height, weight, and age, forexample, can be input to the software application operating on theuser's mobile device, and wirelessly transmitted to the Handheld Sensorfor follow-on analysis (e.g., to calculate V_(c)).

Φa and Z₀ are then used to calculate the resistance (Z₀ cos(Φa)) and thereactance (Z₀ sin(Φa)) of the tissue in the abdomen, chest, and rightarm. Resistance and reactance have been shown to be predictive of tissuecomposition. For example, fatty tissue is far more electricallyconductive than fat-free tissue. Therefore, a tissue's resistance islargely governed by the mass of the fat-free tissue present. This makesthe inverse of a tissue's resistance a good estimator of that tissue'sfat-free mass. Similarly, cell membranes have capacitive properties thatcause phase changes in current that passes through the body. The greaterthe concentration of cells in the tissue, the greater the change inphase. When coupled with resistance, reactance can thus distinguishchanges in fat from changes in fluid due to the differences in thecellularity of fat and extracellular fluid. Specifically, it has beenshown that resistance and reactance—coupled with height, weight andage—can predict fat-free mass and body-fat mass as accurately as the“gold-standard” method—air displacement plethysmography. This isdescribed in the following journal article, the contents of which areincorporated herein by reference: Body fat measurement by bioelectricalimpedance and air displacement plethysmography: a cross-validation studyto design bioelectrical impedance equations in Mexican adults; NutritionJournal; 6: (2007). When fat-free mass, body-fat mass, and weight aremeasured, the root cause of changes in weight can be identified. Changesin fluid retention can signal the onset or reoccurrence of numerousmedical conditions, such as CHF and ESRD. By measuring both reactanceand resistance, both the Floormat and Handheld Sensor can distinguishchanges in fluid retention from changes in tissue mass. This enablesreliable tracking of this important parameter at home, on a daily basis.It also may improve the calculated accuracy of V_(c), thereby improvingthe accuracy in calculating SV and CO

3. Handheld Sensor

The Handheld Sensor 100 works in concert with the Floormat 200 andmobile device 125, as described above. FIGS. 6-8 illustrate the HandheldSensor's measurement electronics and internal components in more detail.In general, a housing of the Handheld Sensor 100 is constructed from twogenerally symmetric, right and left halves 177A, 177B, which are joinedtogether along a longitudinal midline. The housing halves 177A, 177B aresuitably formed (e.g., injection molded) from a rigid material, e.g.,medical-grade plastic. A circuit board 130 is housed within an internalspace formed by the right and left halves 177A, 177B of the HandheldSensor's housing, primarily within the neck 106, and supports theelectronics that drive each measurement. A battery pack 170, includingtwo rechargeable lithium-ion batteries, powers the system. The batteriescan be recharged through a standard USB connector (not shown in thefigure) that connects through a cable to an AC/DC adaptor plugged into awall outlet or, depending on power requirements, a USB port of apersonal computer.

The upper portion of the circuit board 130 extends to within the cavityportion 105 and includes a dual-emitting LED 132, which generates redand infrared optical wavelengths in the 660 nm and 908 nm region, and aphotodetector (e.g., photodiode) 134. These components measure PPGwaveforms using both red and infrared radiation, as is generally knownin the art, but quite advantageously from one of the digits (e.g., thethumb) of the hand with which the user holds the Handheld Sensor. Thismakes for a highly compact, easy-to-use, comprehensive device. A digitalsystem (i.e., microprocessor featuring suitably configured computercode) within the circuit board 130 processes the waveforms to determineSpO2. Generally speaking, such measurement is described in more detailin the following co-pending patent applications, the contents of whichare incorporated herein by reference: “NECK-WORN PHYSIOLOGICAL MONITOR,”U.S. Ser. No. 62/049,279, filed Sep. 11, 2014; “NECKLACE-SHAPEDPHYSIOLOGICAL MONITOR,” U.S. Ser. No. 14/184,616, filed Feb. 19, 2014;and “BODY-WORN SENSOR FOR CHARACTERIZING PATIENTS WITH HEART FAILURE,”U.S. Ser. No. 14/145,253, filed Dec. 31, 2013, FLOORMAT PHYSIOLOGICALSENSOR (U.S. Ser. No. ______, Filed ______); COMBINED FLOORMAT ANDBODY-WORN PHYSIOLOGICAL SENSORS (U.S. Ser. No. ______, Filed ______);HANDHELD PHYSIOLOGICAL SENSOR (U.S. Ser. No. ______, Filed ______);PHYSIOLOGICAL MONITORING SYSTEM FEATURING FLOORMAT AND HANDHELD SENSOR(U.S. Ser. No. ______, Filed ______); and PHYSIOLOGICAL MONITORINGSYSTEM FEATURING FLOORMAT AND WIRED HANDHELD SENSOR. In general and asexplained in greater detail in these incorporated references, during anSpO2 measurement, the digital system alternately powers red and infraredLEDs within the dual-emitting LED 132. This process generates twodistinct PPG waveforms. Using both digital and analog filters, thedigital system extracts AC and DC components from the red (RED(AC) andRED(DC)) and infrared (IR(AC) and IR(DC)) PPG waveforms, which thedigital system then processes to determine SpO2, as described in theabove-referenced patent applications.

To measure TEMP, the Handheld Sensor 100 includes an infraredtemperature sensor 136, which is mounted to an upper, forward-mostportion of the circuit board 130. The infrared temperature sensordetects temperature “looking outwardly” from an upper, outer,forward-facing “nose” portion 138 of the cavity portion 105. Morespecifically, to measure TEMP, the Handheld Sensor 100 is held close tothe user's ear (or forehead) so that the outer portion 138 is adjacentto or pressed up against either the left or right ear (or to theforehead). Because the temperature sensor is positioned where it is, theuser can take a temperature reading with the same device used to measurethe other physiological parameters, and without even having to removethe device from his or her hand to do so. In this configuration, theinfrared temperature sensor 136 detects infrared radiation (e.g.blackbody radiation) emitted from inside the ear (or forehead), which itthen converts to a temperature value using techniques known in the art.Suitably, the temperature sensor 136 is a fully digital system, meaningit receives the infrared radiation with an internal photodetector and,using an internal digital system, converts this to a temperature valuethat it sends through a serial interface (e.g. one based on aconventional UART or I2C interface) for follow-on processing.

A multi-color status LED assembly 175 indicates when the device turnson, a measurement is being taken, a measurement is complete, and dataare being transmitted (e.g., via the cable 102). The multi-color statusLED assembly 175 can change color and blink at different frequencies toindicate these states.

The generally C-shaped or U-shaped, wrist-receiving portion 104 isconfigured to measure physiological parameters using two complementarymeasurement modalities. According to one modality, the C-shaped portionmeasures BP, e.g. SYS, DIA, and MAP, by direct sensing of pressure. Tothat end, the wrist-receiving portion 104 includes a pair ofinflatable/deflatable, elastomeric bladders 140A,B, which are mounted onor supported by the two generally parallel, spaced-apart walls or wings101 a, 101 b that extend from the base 101 c of the wrist-receivingportion 104; the walls form a space or opening in which the user's wristis received. (Other shapes of the bladder-supporting walls are alsoacceptable. For example, even a completely circular, wrist-surroundingring-shaped structure through which the user would insert their armcould be provided.) The bladders 140A,B are configured and arranged toinflate inwardly, i.e., into the wrist-receiving space or opening, asillustrated in FIGS. 8A and 8B. A pair of plastic supports 163A, 163Bhold the inflatable bladders 140A,B in place on their respective walls.Additionally, the plastic supports 163A, 163B clamp down on stretchablecloth electrodes 150A,B, addressed below, which overlie the bladders.

A small pneumatic pump system 142, controlled by the digital system onthe circuit board 130, inflates the bladders 140A,B to measure BP. Ingeneral, such pump systems are known in the art for use in connectionwith blood-pressure monitors such as those typically sold for home use.The pump system 142 includes a diaphragm pump; a solenoid-controlledvalve to maintain or release pressure within the bladders; and suitableairline tubing leading into the bladders. Alternatively, to reduce theweight and/or size of the Handheld Sensor 100, the pneumatic pump andvalves could, instead, be located in the Floormat 200 and provide air tothe inflatable bladders via a tube extending from the Floormat 200 tothe Handheld Sensor 100, preferably along the cable 102.

Gradual inflation of the bladders 140A,B slowly compresses the user'sradial artery. As it compresses, heartbeat-induced blood-flow within theartery generates slight pressure pulsations. These create a smallpressure increase in the bladders that are detected by apressure-measuring system (not shown in the figure) within the circuitboard 130 (or circuit board 206 if the pump is located in the Floormat200), as known in the art. This yields a pressure waveform that featuresamplitudes of the pressure pulsations plotted against the pressureapplied by the inflatable bladders 140A,B. The pressure waveformtypically features a bell-shaped curve when the amplitude of eachpressure pulsation is plotted against the pressure applied. Theappropriate digital system processes the bell-shaped curve to determineblood pressure according to the well-known technique of oscillometry.Such a technique is described in detail in the following co-pendingpatent applications, the contents of which have been previouslyincorporated herein by reference: “NECK-WORN PHYSIOLOGICAL MONITOR,”U.S. Ser. No. 62/049,279, filed Sep. 11, 2014; “NECKLACE-SHAPEDPHYSIOLOGICAL MONITOR,” U.S. Ser. No. 14/184,616, filed Feb. 19, 2014;and “BODY-WORN SENSOR FOR CHARACTERIZING PATIENTS WITH HEART FAILURE,”U.S. Ser. No. 14/145,253, filed Dec. 31, 2013, FLOORMAT PHYSIOLOGICALSENSOR (U.S. Ser. No. ______, Filed ______); COMBINED FLOORMAT ANDBODY-WORN PHYSIOLOGICAL SENSORS (U.S. Ser. No. ______, Filed ______);HANDHELD PHYSIOLOGICAL SENSOR (U.S. Ser. No. ______, Filed ______);PHYSIOLOGICAL MONITORING SYSTEM FEATURING FLOORMAT AND HANDHELD SENSOR(U.S. Ser. No. ______, Filed ______); and PHYSIOLOGICAL MONITORINGSYSTEM FEATURING FLOORMAT AND WIRED HANDHELD SENSOR. To summarize, MAPcorresponds to the applied pressure that yields the maximum amplitude ofthe bell-shaped curve. SYS and DIA are determined, respectively, fromapplied pressures that yield well-defined amplitudes on thehigh-pressure and low-pressure sides of MAP. More specifically, SYStypically corresponds to the applied pressure that yields a pulseamplitude on the high-pressure side of MAP that, when divided by thepulse amplitude corresponding to MAP, has a ratio of about 0.4. DIAtypically corresponds to the applied pressure that yields a pulseamplitude on the low-pressure side of MAP that, when divided by thepulse amplitude corresponding to MAP, has a ratio of 0.6. Other ratioscan also be used to calculate SYS and DIA according to oscillometry.

During inflation, patches of conductive fabric disposed on the outer,wrist-contacting surface of the bladders 140A,B detect biometricsignals. These signals are transmitted along the conductors within thecable 102 and are processed by analog circuitry associated on theFloormat's circuit board 206 to generate ECG and TBI waveforms, asdescribed in more detail above.

The Handheld Sensor 100 can also measure blood pressure according to analternative direct-pressure-based technique. This technique involvesmonitoring PPG waveforms generated by the SpO2 measuring system (i.e.,by either red or infrared wavelengths emitted by the dual-emitting LED132 and detected by the photodetector 134) while the inflatable bladders140A,B apply pressure to the user's radial artery. Here, the appliedpressure slowly reduces blood flow through the artery, causingheartbeat-induced PPG-waveform pulsations (i.e. pulsations in theRED(AC) or IR(AC) components of the PPG waveforms) to slowly increase,and then gradually decrease. As with oscillometry, the maximum amplitudeof the pulsations typically corresponds to an applied pressure equal toMAP. The pulsations are completely eliminated when the applied pressureis equal to SYS, since at this pressure the radial artery is fullyoccluded, thus ceasing all blood flow. DIA can be determined from MAPand SYS using equations described in the above-referenced patentapplications, the contents of which have been previously incorporatedherein by reference.

Believed to be unique to the Handheld Sensor 100, the wrist-contactingelectrodes 150A, 150B are coincident with (i.e., overlie) the inflatablebladders 140A, 140B, respectively, such that the overall system includeswhat are effectively inflatable electrodes. As a result, when thebladders are inflated in connection with measuring BP via direct,mechanical measurement of pressure, the electrodes are pressed firmlyagainst the user's skin, thereby enhancing electrical contact andaccuracy/reliability of the electrophysiological measurements beingtaken. Additionally, such an arrangement facilitates the compact,self-contained form factor of the Handheld Sensor 100.

To this end, and as shown in more detail in FIGS. 8A and 8B, theelectrodes 150A, 150B are formed from a stretchable, conductive fabricthat is stretched over the inflatable bladders. In general, theelectrode material is conductive fabric that has conductive elementsinterwoven in an elastic material. Resistivity is essentially 0 Ohms inboth stretched and unstretched configurations. Suitably, the fabric isable to stretch by at least 25% along at least one dimension when theinflatable bladder is inflated, and preferably it is able to stretch byroughly 50% of its original dimension when force is applied to it.

Both the Floormat and the Handheld Sensor may include a vibratingcomponent to indicate when a measurement is complete. These systems mayalso include accelerometers to detect motion of the user. Thisinformation can be used, for example, to improve measurement quality byselectively detecting an ideal measurement period when motion isminimized. Accelerometers can also be used to detect the user's motionand thus initiate specific measurements, such as measurement of TEMP asdescribed above, and also measurements performed by the Floormat. Thisapproach, for example, would obviate the need for the pushbutton on/offswitch (component 209 in FIG. 4) described above.

4. Other Measurements—Pulse Transit Time

The detection and analysis of each of the above-described physiologicalwaveforms indicates blood flow through the user's body. Morespecifically, the circuitry can analyze the pulsatile components todetermine parameters such as PTT, pulse arrival time (PAT), and vasculartransit time (VTT). Such transit times can be used, for example, tocalculate blood pressure, e.g. SYS, DIA, and MAP. This methodology isdescribed in more detail in the following co-pending patentapplications, the contents of which have been previously incorporatedherein by reference: “NECK-WORN PHYSIOLOGICAL MONITOR,” U.S. Ser. No.62/049,279, filed Sep. 11, 2014; “NECKLACE-SHAPED PHYSIOLOGICALMONITOR,” U.S. Ser. No. 14/184,616, filed Feb. 19, 2014; and “BODY-WORNSENSOR FOR CHARACTERIZING PATIENTS WITH HEART FAILURE,” U.S. Ser. No.14/145,253, filed Dec. 31, 2013, and ‘FLOORMAT PHYSIOLOGICAL SENSOR’,U.S.S.N FLOORMAT PHYSIOLOGICAL SENSOR (U.S. Ser. No. ______, Filed______); COMBINED FLOORMAT AND BODY-WORN PHYSIOLOGICAL SENSORS (U.S.Ser. No. ______, Filed ______); HANDHELD PHYSIOLOGICAL SENSOR (U.S. Ser.No. ______, Filed ______); PHYSIOLOGICAL MONITORING SYSTEM FEATURINGFLOORMAT AND HANDHELD SENSOR (U.S. Ser. No. ______, Filed ______); andPHYSIOLOGICAL MONITORING SYSTEM FEATURING FLOORMAT AND WIRED HANDHELDSENSOR.

To summarize, FIGS. 9A and 9B show the following time-dependentwaveforms, as measured by the Floormat and/or Handheld Sensor: ECG (plot300), ΔZ(t) (plot 302), PPG (plot 304), d(ΔZ(t))/dt (plot 306), andd(PPG)/dt (plot 308). As shown in plots 300 and 302, individualheartbeats produce time-dependent pulses in both the ECG and ΔZ(t)waveforms. As is clear from the data, pulses in the ECG waveform precedethose in the ΔZ(t) waveform. The ECG pulses—each featuring a sharp,rapidly rising QRS complex—mark the beginning of the cardiac cycle.

ΔZ(t) pulses follow the QRS complex by about 100 ms and indicate bloodflow through arteries in the region of the body where the clothelectrodes make contact with the skin. During a heartbeat, blood flowsfrom the user's left ventricle into the aorta; the volume of blood thatleaves the ventricle is the SV. Blood flow periodically enlarges thisvessel, which is typically very flexible, and also temporarily alignsblood cells (called erythrocytes) from their normally randomorientation. Both the temporary enlargement of the vessel and alignmentof the erythrocytes improves blood-based electrical conduction, thusdecreasing the electrical impedance as measured with ΔZ(t). Thed(ΔZ(t))/dt waveform (plot 306) shown in FIG. 9B is a first mathematicalderivative of the raw ΔZ(t) waveform, meaning its peak represents thepoint of maximum impedance change.

A variety of time-dependent parameters can be extracted from the ECG andTBI waveforms. For example, as noted above, it is well know that HR canbe determined from the time separating neighboring ECG QRS complexes.Likewise, left ventricular ejection time (LVET) can be measured directlyfrom the derivative of pulses within the ΔZ(t) waveform, and isdetermined from the onset of the derivatized pulse to the firstpositive-going zero crossing. Also measured from the derivatized pulsesin the ΔZ(t) waveform is (dΔZ(t))/dt)_(max), which is a parameter usedto calculate SV as described above.

The time difference between the ECG QRS complex and the peak of thederivatized ΔZ(t) waveform represents a pulse arrival time PAT, asindicated in FIGS. 9A and 9B. This value can be calculated from otherfiducial points, including, in particular, locations on the ΔZ(t)waveform such as the base, midway point, or maximum of theheartbeat-induced pulse. Typically, the maximum of the derivatizedwaveform is used to calculate PAT, as it is relatively easy to develop asoftware beat-picking algorithm that finds this fiducial point.

PAT correlates inversely to SYS, DIA, and MAP, which can be calculatedas described in the above-referenced patent applications usinguser-specific slopes for SYS and DIA, measured during a calibrationmeasurement. (Such a measurement can, for example, be performed with theinflatable bladders and optical systems described above.) Without thecalibration, PAT only indicates relative changes in SYS, DIA, and MAP.The calibration yields both the user's immediate values of theseparameters. Multiple values of PAT and blood pressure can be collectedand analyzed to determine user-specific slopes, which relate changes inPAT with changes in SYS, DIA, and MAP. The user-specific slopes can alsobe determined using pre-determined values from a clinical study, andthen combining these measurements with biometric parameters (e.g. age,gender, height, weight) collected during the clinical study.

In embodiments of the Handheld Sensor, waveforms like those shown inFIGS. 9A and 9B can be processed to determine transit times such as PATand VTT. The Floormat and/or Handheld Sensor can use these parameters,combined with a calibration determined as described above, to calculateblood pressure without a mechanism that applies pressure, e.g. theinflatable bladders described above. Typically PAT and SYS correlatebetter than PAT and DIA.

PP can be used to calculate DIA from SYS, and can be estimated fromeither the absolute value of SV, SV modified by another property (e.g.LVET), or the change in SV. In the first method, a simple linear modelis used to process SV (or, alternatively, SV×LVET) and convert it intoPP. The model uses the instant values of PP and SV, determined asdescribed above from a calibration measurement, along with a slope thatrelates PP and SV (or SV×LVET) to each other. The slope can be estimatedfrom a universal model that, in turn, is determined using a populationstudy.

Alternatively, a slope tailored to the individual user can be used. Sucha slope can be selected, for example, using biometric parameterscharacterizing the user as described above.

Here, PP/SV slopes corresponding to such biometric parameters aredetermined from a large population study and then stored in computermemory on the Floormat and/or Handheld Sensor. When a device is assignedto a user, their biometric data is entered into the system, e.g. using aGUI operating on a mobile device, that transmits the data to theFloormat and/or Handheld Sensor via Bluetooth®. Then, an algorithmprocesses the data and selects a user-specific slope. Calculation of PPfrom SV is explained in the following reference, the contents of whichare incorporated herein by reference: “Pressure-Flow Studies in Man. AnEvaluation of the Duration of the Phases of Systole,” Harley et al.,Journal of Clinical Investigation, Vol. 48, p. 895-905, 1969. Asexplained in this reference, the relationship between PP and SV for agiven user typically has a correlation coefficient r that is greaterthan 0.9, which indicates excellent agreement between these twoproperties. Similarly, in the above-mentioned reference, SV is shown tocorrelate with the product of PP and LVET, with most users showing an rvalue of greater than 0.93 and the pooled correlation value (i.e., thecorrelation value for all subjects) being 0.77. This last valueindicates that a single linear relationship between PP, SV, and LVET mayhold for all users.

More preferably, PP is determined from SV using relative changes inthese values. Typically, the relationship between the change in SV andchange in PP is relatively constant across all subjects. Thus, similarto the case for PP, SV, and LVET, a single, linear relationship can beused to relate changes in SV and changes in PP. Such a relationship isdescribed in the following reference, the contents of which areincorporated herein by reference: “Pulse pressure variation and strokevolume variation during increased intra-abdominal pressure: anexperimental study,” Didier et al., Critical Care, Vol. 15:R33, p. 1-9,2011. Here, the relationship between PP variation and SV variation for67 subjects displayed a linear correlation of r=0.93, which is anextremely high value for pooled results that indicates a single, linearrelationship may hold for all users.

From such a relationship, PP can be determined from the impedance-basedSV measurement, and SYS can be determined from PAT. DIA can then becalculated from SYS and PP.

Another parameter, VTT, can be determined from pulsatile components inthe ΔZ(t) (or d(ΔZ(t))/dt) waveform and the PPG (or d(PPG)/dt) waveform.FIGS. 9A and 9B show in more detail how VTT is determined. It can beused in place of PAT to determine blood pressure, as described above.Using VTT instead of PAT in this capacity offers certain advantages,namely, lack of signal artifacts such as pre-injection period (PEP) andisovolumic contraction time (ICT), which contribute components to thePAT value but which are not necessarily sensitive to or indicative ofblood pressure.

Alternatively, the pulsations in the BCG waveform can be processed asdescribed above to calculate PTT, PAT, and/or VTT.

In general, the overarching purpose of a system that combines theFloormat and Handheld Sensor according to the invention, as describedabove, is to make daily measurements of a wide range of physiologicalparameters that, in turn, can be analyzed to diagnose specific diseasestates. Use of a single system, as opposed to multiple devices, cansimplify operation and reduce the time required to measure theabove-mentioned parameters. This, in turn, may increase the user'scompliance, as it is well established that daily use of devices thatmeasure physiological parameters typically improves as the time andcomplexity required for such devices decreases.

By consistently collecting physiological information on a daily basis,the combined Floormat and Handheld Sensor can calculate trends in theinformation. Such trends may indicate the progression of certain diseasestates in a manner that is improved relative to one-time measurements ofcertain parameters. For example, a value of fluids corresponding to 15Ohms, or an SV corresponding to 75 mL, has little value taken inisolation. But if these parameters decrease by 20% over a period of afew days, it can indicate that the user's heart is pumping blood in aless efficient manner (as indicated by the SV), which in turn decreasesperfusion of their kidneys and causes them to retain more fluids (asindicated by the fluid level).

In this regard, FIG. 10 shows, for example, a table 400 indicating howtrends in different physiological parameters can be used to diagnosedisease states such as hypertension, cardiac disease, HF (includingCHF), renal failure (including ESRD), COPD, diabetes, and obesity. Inaddition, the table 400 indicates how such trends may show beneficialprogress to a population actively involved in exercise.

Still other embodiments are within the scope of the invention. Forexample, both the Handheld Sensor and Floormat can take on mechanicalconfigurations that are different than those shown in FIGS. 1 and 4-8.For example, the flexible cable that connects the Floormat and HandheldSensor may be replaced by a rigid component, such as a vertical plasticcomponent that encloses the cable. The vertical plastic component mayinclude handles that include the electrodes. The Handheld Sensor may bereplaced by a patch or similar component, including both optics andelectrodes, which attaches to the user's chest, as opposed to being heldin the user's hand. The electrodes in the Handheld Sensor may beexclusively in the Sensor's grip and not disposed on top of theinflatable bladders, as is the case of the Handheld Sensor shown in FIG.5. With such a configuration, BP would be determined strictly byprocessing PTT, PAT, and/or VTT as described above. Here, electrodes maybe fabricated from either disposable or reusable components. Likewise,the Handheld Sensor, and not the Floormat, may include an electrode usedfor the right leg drive circuit. The Floormat may also include amechanical, optical, or electrical mechanism configured to measure theuser's height. Algorithms that process time-dependent physiologicalwaveforms, such as ECG, TBI, PPG, BR, BCG, and pressure waveforms, maybe different than those described herein, granted they perform a similarfunction of calculating a physiological parameter, e.g. a vital sign orhemodynamic parameter. Likewise, a pulse transit time, such as a PAT orVTT, can be calculated from one or more pulsatile components selectedfrom one or more of the time-dependent physiological waveforms describedherein.

In other embodiments, the Floormat described above can integrate with a‘patch’ that directly adheres to a portion of a patient's body, or a‘necklace’ that drapes around the patient's neck. The patch would besimilar in form to the necklace's base, although it may take on othershapes and form factors. It would include most or all of the samesensors (e.g. sensors for measuring ECG, TBI, and PPG waveforms) andcomputing systems (e.g. microprocessors operating algorithms forprocessing these waveforms to determine parameters such as HR, HRV, RR,BP, SpO2, TEMP, CO, SV, fluids) as the base of the necklace. Howeverunlike the system described above, the battery to power the patch wouldbe located in or proximal to the base, as opposed to the strands in thecase of the necklace. Also, in embodiments, the patch would include amechanism such as a button or tab functioning as an on/off switch.Alternatively, the patch would power on when sensors therein (e.g. ECGor temperature sensors) detect that it is attached to a patient.

In typical embodiments, the patch includes a reusable electronics module(shaped, e.g., like the base of the necklace) that snaps into adisposable component that includes electrodes similar to those describedabove. The patch may also include openings for optical and temperaturesensors as described above. In embodiments, for example, the disposablecomponent can be a single disposable component that receives thereusable electronics module. In other embodiments, the reusableelectronics module can include a reusable electrode (made, e.g., from aconductive fabric or elastomer), and the disposable component can be asimple adhesive component that adheres the reusable electrode to thepatient.

In preferred embodiments the patch is worn on the chest, and thusincludes both rigid and flexible circuitry, as described above. In otherembodiments, the patch only includes rigid circuitry and is designed tofit on other portions of the patient's body that is more flat (e.g. theshoulder).

In embodiments, for example, the system described above can calibratethe patch or necklace for future use. For example, the Floormat candetermine a patient-specific relationship between transit time and bloodpressure, along with initial values of SYS, DIA, and MAP. Collectivelythese parameters represent a cuff-based calibration for blood pressure,which can be used by the patch or necklace for cuffless measurements ofblood pressure. In other embodiments, the Floormat can measure afull-body impedance measurement and weight. These parameters can bewirelessly transmitted to the necklace or patch, where they are usedwith their impedance measurement to estimate full-body impedance (e.g.during a dialysis session). Additionally, during the dialysis session,the necklace or patch can use the values of full-body impedance andweight to estimate a progression towards the patient's dry weight.

These and still other embodiments of the invention are deemed to bewithin the scope of the following claims.

What is claimed is:
 1. A biometric sensor system configured to measure aphysiological parameter, comprising: a first device comprising agenerally flat Floormat configured to rest stably on a generally flatsurface and to support the weight of a user standing thereon, theFloormat including first and second electrodes disposed at an uppersurface thereof and in position to make contact with the sole of one ofthe user's feet when the user stands on the Floormat; and a seconddevice comprising a Handheld Sensor configured to be supported at aregion of one of the user's hands, the Handheld Sensor 1) includingthird and fourth electrodes disposed in position to make contact withskin in the region of the user's hand when the Handheld Sensor issupported thereat; and 2) being electrically connected to the Floormatvia a cable having one or more electrical conductors disposed therein;the first and third electrodes being configured to inject electricalcurrent into the user at their respective points of contact with theuser and the second and fourth electrodes being configured to sensefirst and second biometric signals, respectively, which are induced bythe injected electrical current; the biometric sensor system furthercomprising a first analog system configured to receive the first andsecond biometric signals and to process them to generate first andsecond analog physiological waveforms; and a digital system configuredto digitize the analog physiological waveforms and to process them withcomputer code to determine the physiological parameter; wherein thefirst analog system is located in one of the first and second devicesand the electrodes disposed in the other device are electricallyconnected to the first analog system by means of said one or moreelectrical conductors.
 2. The biometric sensor system of claim 1,wherein the first analog system comprises a differential amplifierconfigured to amplify a difference between the first and secondbiometric signals to generate the first and second analog physiologicalwaveforms.
 3. The biometric sensor system of claim 2, wherein the firstand second analog physiological waveforms are impedance waveforms, andwherein the first analog waveform comprises AC information and thesecond physiological waveform comprises DC information.
 4. The biometricsensor system of claim 3, wherein the first analog waveform comprisesheartbeat-induced pulsations.
 5. The biometric sensor system of claim 3,wherein the physiological parameter is stroke volume.
 6. The biometricsensor system of claim 1, wherein the computer code is configured toprocess the first analog physiological waveform to calculate aderivative and determine a dΔZ(t)/dt waveform.
 7. The biometric sensorsystem of claim 6, wherein the computer code is configured to determinea maximum value of the dΔZ(t)/dt waveform.
 8. The biometric sensorsystem of claim 6, wherein the computer code is configured to determinean area of a pulse in the dΔZ(t)/dt waveform.
 9. The biometric sensorsystem of claim 6, wherein the computer code is configured to estimatean ejection time from the dΔZ(t)/dt waveform.
 10. The biometric sensorsystem of claim 9, wherein the computer code is configured to determinei) a maximum value of the dΔZ(t)/dt waveform ((dΔZ(t)/dt)_(max)), andii) a left ventricular ejection time (LVET) from the dΔZ(t)/dt waveform.11. The biometric sensor system of claim 6, wherein the computer code isconfigured to process the second analog physiological waveform toestimate a baseline impedance (Z₀).
 12. The biometric sensor system ofclaim 11, wherein the computer code is configured to determine strokevolume (SV) from the equation:${S\; V} = {V_{c} \times \frac{\left( {d\; \Delta \; {{Z(t)}/{dt}}} \right)_{\max}}{Z_{o}} \times L\; V\; E\; T}$where V_(c) is a volume conductor calculated from a weight value. 13.The biometric sensor system of claim 12, wherein the Floormat includes aweight-measurement subsystem comprising at least one load cell, theweight-measurement subsystem configured to determine the weight value.14. The biometric sensor system of claim 11, wherein the computer codeis configured to determine stroke volume (SV) from the equation:${S\; V} = {V_{c} \times \sqrt{\frac{\left( {d\; \Delta \; {{Z(t)}/{dt}}} \right)_{\max}}{Z_{o}}} \times L\; V\; E\; T}$where V_(c) is a volume conductor calculated from a weight value. 15.The biometric sensor system of claim 14, wherein the Floormat includes aweight-measurement subsystem comprising at least one load cell, theweight-measurement subsystem configured to determine the weight value.16. The biometric sensor system of claim 1, further comprising a circuitboard disposed within each of the Floormat and the Handheld Sensor. 17.The biometric sensor system of claim 16, wherein the analog and digitalsystems are disposed on the circuit board disposed within the Floormatand the digital system includes a microprocessor that is programmed withsaid computer code to process the analog physiological waveforms todetermine the physiological parameter.
 18. The biometric sensor systemof claim 17, wherein the first, second, third, and fourth electrodes arein electrical, signal-conducting contact with the analog system.
 19. Thebiometric sensor system of claim 16, wherein the analog and digitalsystems are disposed on the circuit board disposed within the HandheldSensor and the digital system includes a microprocessor that isprogrammed with said computer code to process the analog physiologicalwaveforms to determine the physiological parameter.
 20. The biometricsensor system of claim 19, wherein the first, second, third, and fourthelectrodes are in electrical, signal-conducting contact with the analogsystem.
 21. The biometric sensor system of claim 1, wherein the HandheldSensor includes a grip that can be grasped with the user's hand tosupport the Handheld Sensor and the third and fourth electrodes aredisposed at the grip such that the third and fourth electrodes makescontact with the user's palm and/or anterior surfaces of the user'sfingers when the user grasps the grip.
 22. The biometric sensor systemof claim 1, wherein the Handheld Sensor includes an arm-receivingportion configured to receive therein a distal portion of the user's armthat is located at said region of the user's hand and the third andfourth electrodes are disposed at said arm-receiving portion such thatthe third and fourth electrodes make contact with the distal portion ofthe user's arm when the distal portion of the user's arm is receivedwithin the arm-receiving portion.
 23. The biometric sensor system ofclaim 22, wherein the arm-receiving portion comprises an inflatable cuffconfigured to receive and engage the distal portion of the user's arm.24. The biometric sensor system of claim 23, wherein the cuff comprisesan inflatable bladder.
 25. The biometric sensor system of claim 24,wherein the third and fourth electrodes are formed from conductive,elastomeric material disposed over a surface of the inflatable bladder.26. The biometric sensor system of claim 24, wherein the biometricsensor system further comprises a microprocessor-controlled pneumaticinflation system configured and arranged to control inflation anddeflation of the inflatable bladder.
 27. The biometric sensor system ofclaim 26, wherein the third and fourth electrodes are formed fromelastomeric fabric that stretches and contracts with the inflatablebladder as the bladder is inflated and deflated.
 28. The biometricsensor system of claim 1, wherein the first, second, third, and fourthelectrodes each comprise a conductive material.
 29. The biometric sensorsystem of claim 28, wherein the conductive material comprising the firstelectrode is one of a conductive fabric, a metal component, a conductivefoam, a conductive polymeric material, and a hydrogel material; theconductive material comprising the second electrode is one of aconductive fabric, a metal component, a conductive foam, a conductivepolymeric material, and a hydrogel material; the conductive materialcomprising the third electrode is one of a conductive fabric, a metalcomponent, a conductive foam, a conductive polymeric material, and ahydrogel material; and the conductive material comprising the fourthelectrode is one of a conductive fabric, a metal component, a conductivefoam, a conductive polymeric material, and a hydrogel material.